Rectifying device and method for manufacturing the same

ABSTRACT

Disclosed herein are a rectifying device and a method of fabricating the same. The rectifying device includes a first electrode formed in a flat shape, an insulating layer deposited on the first electrode and a second electrode formed on a preset region of the insulating layer in a nanaopillar shape in a longitudinal direction to be asymmetrical to the first electrode, thereby increasing current flow.

CROSS-REFERENCES TO RELATED APPLICATION

This patent application claims the benefit of priority from KoreanPatent Application No. 10-2013-0057073, filed on May 21, 2013, thecontents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to a rectifying device and a method formanufacturing the same, and more particulary, to an asymmetricrectifying device and a method for manufacturing the same.

2. Description of the Related Art

As a rectifying device having a rectifying property, there is a siliconor germanium diode using a p-n junction of a semiconductor, or aselenium rectifier or a copper oxide rectifier using the contact surfaceof the metal and the semiconductor. For example, there is a tunneldiode, etc.

Since the tunnel diode was invented by Esaki Leona, it has continuouslyreceived attention for half a century.

The tunnel diode is preferable for maintaining any switching state suchas an open/closed state in many application fields, and a function ofthe tunnel diode is based on an interband tunneling of charge carriers.

For example, a tunnel diode is disclosed in Korean

Patent Publication No. 1995-0021729 entitled “tunnel diode and memorydevice”. In this tunnel diode, an insulating dielectric material isinserted between two conductive metal electrodes, forms a barrier havinga barrier level for electrons and has a ferroelectric material layer atroom temperature, in the tunnel diode having a degree of thickness suchthat electrons can tunnel through the barrier from one electrode to theother electrode at a voltage higher than a threshold voltage, and acurrent polarization of the dielectric material has a property in thatit may vary the barrier level.

Also, a stacked solar cell having a tunnel diode layer is disclosed inKorean Patent Publication No. 2005-0065028 entitled “stacked solar cellhaving tunnel diode layer”. This stacked solar cell having the tunneldiode layer is configured to include a GaAlAs upper cell having a windowlayer on an upper surface on which light is incident, a GaAs lower cellto which a carrier generated in the GaAlAs upper cell transfers and atunnel diode installed between the GaAlAs upper cell and the GaAs lowercell.

Further, a solar cell having a p-n tunnel diode is disclosed in KoreanPatent No. 10-1105250 entitled “solar cell having p-n tunnel diode”. Thesolar cell having the p-n tunnel diode includes an n-type substrate, ap-n tunnel diode formed on the n-type substrate in which an n-typesemiconductor and a p-type semiconductor are sequentially stacked toform a p-n junction, a photoelectric conversion cell formed on the p-ntunnel diode wherein the n-type semiconductor and the p-typesemiconductor are sequentially stacked to convert a photo signal to aelectrical signal, a lower electrode formed on a lower portion of then-type substrate and an upper electrode formed on the photoelectricconversion cell, wherein the lower electrode and the upper electrode aren-ohmic contact electrodes.

In the tunnel diode such as that in this embodiment, when a voltage isapplied across the junction and the tunnel diode is forward biased, asthe voltage increases up to a peak voltage, a current increases up to apeak current, and if the voltage further increases up to a valleyvoltage, the current decreases up to a valley current.

However, the tunnel diode is considered to have a potential equal to atransistor, but does not actually have the potential in actualapplications.

Using the tunnel diode has many potential advantages in manyapplications, but may limit application diversity because ofinsufficient performance due to the technical limits of a fabricationand a driving mechanism. Due to recent increases in data volume andcommunication frequencies, the development of a tunnel diode capable ofoperating in ultrahigh frequencies is required.

SUMMARY OF THE INVENTION

A rectifying device according to an embodiment of the present inventionincludes a first electrode formed in a flat shape, an insulating layerdeposited on the first electrode and a second electrode formed on apreset region of the insulating layer in a different shape from thefirst electrode in a longitudinal direction to be asymmetrical to thefirst electrode, thereby increasing current flow.

Also, the first electrode is formed of any one of a metal, asemiconductor or a graphene.

Further, the second electrode 30 is formed of any one of a nanotube or ananowire having an aspect ratio of 200:1 to 2000:1.

Furthermore, the nanotube is formed of any one of a carbon nanotube, ametallic nanotube and a semiconductive nanotube, wherein a cross-sectionof the nanotube is any one of a ring shape, a square, a rectangul and anoval.

Also, the nanowire is formed of any one of a metallic nanowire or asemiconductive nanowire, wherein a cross-section of the nanowire is anyone of a ring shape, a square, a rectangul and an oval.

Meanwhile, a method of fabricating a rectifying device according to anembodiment includes a step of forming a first electrode having a flatshape, a step of forming a insulating layer on the first electrode and astep of forming a second electrode layer having a different shape fromthe first electrode in a longitudinal direction on a preset region ofthe insulating layer.

A rectifying device according to another embodiment of the presentinvention includes a first electrode and a contact electrode spaced apredetermined distance apart from each other on a substrate and a secondelectrode spaced apart from the first electrode, and connected to thecontact electrode, wherein the first electrode is a flat shape and thesecond electrode is formed on a preset region of the insulating layer ina different shape from the first electrode in a longitudinal direction,so that the first electrode and the second electrode are asymmetrical toeach other.

A rectifying device according to a further embodiment of the presentinvention includes a first electrode and a contact electrode spaced apredetermined distance apart from each other on a substrate, a secondelectrode spaced apart from the first electrode and connected to thecontact electrode and an insulating layer formed to surround a part ofeach of the first electrode and the second electrode including a regionin which the first electrode and the second electrode are spaced apartfrom each other, wherein the first electrode is of a flat shape, and thesecond electrode is formed on a preset region of the insulating layer ina different shape from the first electrode in a longitudinal direction,so that the first electrode and the second electrode are asymmetrical toeach other.

BREIF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a view illustrating a tunnel diode according to a firstembodiment;

FIG. 2 is a cross-sectional view illustrating a tunnel diode accordingto a first embodiment;

FIG. 3 is a graph showing a current flow increase as a result ofoperating a tunnel diode one to three times according to a firstemebodiment;

FIGS. 4 a to 4 l are views illustrating a method of fabricating a tunneldiode according to first and second embodiments;

FIG. 5 is a view illustrating a tunnel diode according to a thirdembodiment; and

FIG. 6 is a view illustrating a tunnel diode according to a fourthembodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a preferred embodiment of the present invention will bedescribed in detail with the reference to the accompanying drawings.

FIG. 1 is a view illustrating a tunnel diode according to a firstembodiment, FIG. 2 is a cross-sectional view illustrating a tunnel diodeaccording to a first embodiment. Also, FIG. 3 is a graph showing acurrent flow increase as a result of operating a tunnel diode one tothree times according to a first emebodiment.

As shown in FIGS. 1 and 2, a tunnel diode according to a firstembodiment includes a first electrode 10, an insulating layer 20deposited on the first electrode 10, a second electrode 30 growing in anano size on the insulating layer 20 and formed asymmetrically to thefirst electrode 10. The asymetrical structure means a structure relatingto the second electode 30 formed in a longitudinal direction pillarshape on the first electrode 10 that is formed in a flat electrode.Also, the second electrode 30 is preferably formed to be perpendicularto the insulating layer 20.

Here, conductive materials such as a metal, a semiconductor, a grapheneor the like may be used in the first electrode 10.

The second electrode 20 is formed of a naonotube or a nanowire having ahigh aspect ratio (height to width) of at least 200:1 to 2000:1.

A carbon nanotube, a metal nanotube, a semiconductive nanotube or thelike my be used in the nanotube.

A metal nanowire, a semiconductive nanowire or the like may be used inthe nanowire.

The nanotube or the nanowire is in a rod-like shape having twoorthogonal cross-sectional dimensions less than 5 nm to 500 nm at anypoint along a longitudinal direction. A cross-section of the nanotube orthe nanowire includes a ring shape, a square, a rectangle or an oval,but is not limited to these shapes and on the contrary, may have anyshape. The cross-section of the nanotube or the nanowire may have aregular or irregular shape.

As shown in FIGS. 2 and 3, the tunnel diode according to the firstembodiment including the second electrode 30 formed of the nanotube orthe nanowire and formed asymmetrically to the first electrode 10 mayincrease a current flow because a strong electric field can be appliedat the same voltage to lower a tunneling barrier, through a field effecttunneling property using the asymmetric structure, that is, the highaspect ratio of the nanotube or the nanowire as well as a work functiondifference according to differences in materials.

A tunneling rate of the tunnel diode is inversely exponential to abarrier height, and a barier thickness formed by a bandgap between aconduction band and a valence band. The thickness is provided by thewidth of a depletion region and by a doping concentration of a material.Also, the mass of electrons and holes is important for the tunnelingrate.

At the point of zero voltage, a junction functions as an ohmicresistance, and the resistance in this analogue is inverselyproportional to the tunneling rate. At the point of peak voltage, thevoltage applied across the junction induces a maximum overlap betweenfree electrons in the conduction band and free holes in the valence bandat the same energies. At this point, the current is a maximum value, andin this state, when the voltage further increases, the currentdecreases. This means that the junction indicates a negativedifferential resistance. However, when the much higher voltage isapplied, the tunnel diode reaches a forward biased normal diode state,and at this time, as the voltage increases, the current increases.

Thus, as shown in the following equation, in the tunnel diode accordingto the first embodiment, the second electrode is formed of the nanotubeor the nanowire, formed asymmetrically to the first electrode 10 andmakes contact with the insulating layer 20. Therefore, because of theasymmetrical structure such as β as well as a work function according toa difference in materials such as φ at the same voltage such as E_(F), astrong electric field may be applied to lower a tunneling barrier,thereby increasing a current flow.

${{PE}_{C\rightarrow O}(x)} = {\left( {E_{F} + \Phi} \right) - \frac{e^{2}}{16\; \pi \; ɛ_{0}x} - {\beta \; e\; x\; E}}$

Here, the PE is a potential energy, the E_(F) is a fermi level energy,the φ is a work function, the ε₀ is an absolute dielectric constant, theβ is a distance from one end of the second electrode 30 contacting aninsulating layer 20 to the other end of the second electrode 30 facingthe one end, and the E is an electric field.

Hereinafter, a method of fabricating a tunnel diode according to a firstembodiment will be described.

FIGS. 4 a to 4 e are views illustrating the method of fabricating thetunnel diode according to the first embodiment. Referring to 4 a to 4 e,in the tunnel diode according to the first embodiment, a silicon oxide(SiO₂) layer 3 is deposited on a substrate.

Also, a first conductive layer 10′ and an insulating layer 20″ aresequently deposited on the silicon oxide layer 3, and then the firstconductive layer 10′ and the insulating layer 20 are etched using aphotolithographic process. Here, a first electrode 10 on which thetunnel diode is to be formed is formed by selectively etching the firstconductive layer 10′ and the insulating layer 20″.

Furthemore, the insulating layer 20 is formed by selectively etching theinsulating layer 20′.

A second electrode 30 is formed on the insulating layer 20. The secondelectrode 30 may be formed in a longitudinal direction using anepitaxial process.

In more detail, the second electrode 30 is formed of an upright nanotubeor nanowire having a high aspect ratio (height to width) of at least200:1 to 2000:1.

Therefore, the first electrode 10 formed in a flat shape and the secondelectrode 30 formed in a different shape from the first electrode 10 ina longitudinal direction are asymmetrical to each other.

Also, the nanowire may grow in a different manner from a mannerdescribed herein.

Herinafter, a method of fabricating a tunnel diode according to a secondembodiment will be described.

When the processes of FIGS. 4 f to 4 l are performed after the processesof FIGS. 4 a to 4 e, FIGS. 4 f to 4 l are views illustrating the methodof fabricating the tunnel diode according to the second embodiment. Aninterlayer insulating film 32 is deposited on an entire surfaceincluding the second electrode 30. After that, regions of the interlayerinsulating film 32 and the insulating layer 20 to which the firstelectrode (10) is electrically connected are selectively etched using aphotolithographic process. Here, at least in part of the first electrode10 is exposed by selectively etching the interlayer insulating film 32.

Further, the interlayer insulating film 32 on the second electrode 30 isetched so that the second electrode 30 is exposed. And then, a bakeprocess is performed on the entire surface including the exposed secondelectrode 30.

After the bake process is performed, a second photoresist layer 34 isapplied on the entire surface including the second electrode 30. Thesecond photoresist layer 34 may be applied at a uniform height. Also,the second photoresist layer 34 is selectively exposed and developed sothat the interlayer insulating film 32 of a region on which a contactelectrode 40 electrically contacted to the second electrode 30 is to beformed is exposed.

A second conductive layer 36 for forming the contact electrode 40electrically connected to the second electrode 30 is deposited on theentire surface including the second photoresist film 34. The secondphotoresist film 34 is removed using a lift-off process to form acontact electrode 40.

Here, the contact electrode 40 is supported by the interlayer insulatingfilm 32, thereby enabling the contact electrode 40 to be electricallycontacted to the second electrode 30 more easily than being directlyelectrically connected to the second electrode 30.

Furthermore, in the tunnel diodes according to the first and the secondembodiments, a tunneling phenomenon may occur between the firstelectrode 10 and the second electrode 30. That is, the tunnelingphenomeon may occur between the first electrode 10 and the secondelectrode 30 with the insulating layer 20 in-between.

Hereinafter, a tunnel diode according to a third embodiment will bedescribed.

FIG. 5 is a view illustrating the tunnel diode according to the thirdembodiment.

Referring to FIG. 5, the tunnel diode according to the third embodimentincludes a first electrode 10 and a contact electrode 40 spaced apredetermined distance apart from each other on a substrate (not shown)on which a silicon oxide layer is formed (not shown) and a secondelectrode 30 spaced apart from the first electrode 10, connected to thecontact electrode 40 and being asymmetrical.

Here, the symmetrical structure means a structure relating the secondelectrode 30 formed in a relative longitudinal direction in a nanopillarshape on the first electrode 10 formed in a flat shape. Furthermore, thesecond electrode 30 is preferably formed perpendicular to the firstelectrode 10 and the contact electrode 40.

In more detail, the first electrode 10 and the contact electrode 40 isspaced apart from each other—for example, each of a left surface of thefirst electrode 10 and a right surface of the contact electrode 40 maybe a facing surface in FIG. 5. In this case, the second electrode 30 maybe formed perpendicular to the right surface of the first electrodewhich is the facing surface and formed perpendicular to the left surfaceof the contact electrode 40.

Furthermore, the second electrode 30 is surrounded by air or a vacuuminstead of the insulating layer 20 of the tunnel diode according to thefirst embodiment. That is, the tunneling phenomeon may occur between thefirst electrode 10 and the second electrode 30 with the air or thevacuum in-between.

Hereinafter, a tunnel diode according to a fourth embodiment will bedescribed.

FIG. 6 is a view illustrating the tunnel diode according to the fourthembodiment.

Referring to FIG. 6, the tunnel diode according to the fourth embodimentincludes a first electrode 10 and a contact electrode 40 spaced apredetermined distance apart from each other on a substrate (not shown)on which a silicon oxide layer is formed (not shown) and a second secondelectrode 30 spaced apart from the first electrode 10, connected to thecontact electrode 40 and being asymmetrical.

Here, the asymmetrical structure means a structure relating to thesecond electrode 30 formed in a relative longitudinal direction in ananopillar shape on the first electrode 10 formed in a flat shape.Furthermore, the second electrode 30 is preferably formed perpendicularto the first electrode 10 and the contact electrode 40.

In more detail, the first electrode 10 and the contact electrode 40 arespaced apart from each other—for example, each of a left surface of thefirst electrode 10 and a right surface of the contact electrode 40 maybe a facing surface in FIG. 6. In this case, the second electrode 30 maybe formed perpendicular to the right surface of the first electrodewhich is the facing surface and formed perpendicular to the left surfaceof the contact electrode 40.

Furthermore, the insulating layer 20 of the tunnel diode according tothe first embodiment is formed in order to surround a part of each ofthe first electrode 10 and the second electrode 30 including a regionwhere the first electrode 10 and the second electerode 30 are spacedapart from each other. That is, the tunneling phenomeon may occurbetween the first electrode 10 and the second electrode 30 with theinsulating layer 20 in-between.

As described above, in a rectifying device and a method formanufacturing the same according to the present invention, one electrodeis formed of a nanotube or a nanowire so that a tunnel diode is anasymmetrical structure, and thus a current flow may increase because astrong electric field can be applied at the same voltage in a highaspect ratio of the nanotube or the nanowire to lower a tunnelingbarrier using a property of field effect tunneling using an asymmetricalstructure as well as a work function difference according to differencesin materials—that is, a high aspect ratio of the nanotube or thenanowire.

In the rectifying device and the method of fabricating the sameaccording to the present invention, since one electrode is formed of ananotube or a nanowire so that a tunnel diode is asymmetrical, thetunnel diode may operate in a super high frequency by rectifying acurrent due to the asymmetrical structure as well as a work functiondifference according to differences in materials.

The object of the present invention is not limited to the aforesaid, andother objects not described herein will be clearly understood by thoseskilled in the art from descriptions below.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims. For example, each of elementsshown in embodiments may be modified and carried out. Also, alldifferences relating to the modifications, additions and substitutionswill be construed as being included in the present invention.

What is claimed is:
 1. A rectifying device comprising: a first electrodeformed in a flat shape; an insulating layer deposited on the firstelectrode; and a second electrode formed in a longitudinal direction ona preset region of the insulating layer in a different shape from thefirst electrode to be asymmetrical to the first electrode, to increasecurrent flow.
 2. The rectifying device of claim 1, wherein the firstelectrode is formed of any one of a metal, a semiconductor or agraphene.
 3. The rectifying device of claim 1, wherein the secondelectrode is formed of any one of a nanotube or a nanowire having anaspect ratio of 200:1 to 2000:1.
 4. The rectifying device of claim 3,wherein the nanotube is formed of any one of a carbon nanotube, ametallic nanotube and a semiconductive nanotube, wherein a cross-sectionof the nanotube is any one of a ring shape, a square shape, arectangular shape and an oval shape.
 5. The rectifying device of claim3, wherein the nanowire is formed of any one of a metallic nanowire or asemiconductive nanowire, wherein a cross-section of the nanowire is anyone of a ring shape, a square shape, a rectangular shape and an ovalshape.
 6. A rectifying device comprising: a first electrode and acontact electrode spaced predetermined distances apart from each otheron a substrate; and a second electrode spaced apart from the firstelectrode and connected to the contact electrode, wherein the firstelectrode is of a flat shape, and the second electrode is formed in alongitudinal direction on a preset region of the insulating layer in adifferent shape from the first electrode, so that the first electrodeand the second electrode are asymmetrical to each other.
 7. A rectifyingdevice comprising: a first electrode and a contact electrode spaced apredetermined distance apart from each other on a substrate; a secondelectrode spaced apart from the first electrode and connected to thecontact electrode; and an insulating layer formed to surround a part ofeach of the first electrode and the second electrode including a regionin which the first electrode and the second electrode are spaced apartfrom each other, wherein the first electrode is of a flat shape, and thesecond electrode is formed in a longitudinal direction on a presetregion of the insulating layer in a different shape from the firstelectrode, so that the first electrode and the second electrode areasymmetrical to each other.
 8. A method of fabricating a rectifyingdevice, the method comprising: a step of forming a first electrodehaving a flat shape; a step of forming an insulating layer on the firstelectrode; and a step of forming a second electrode layer having adifferent shape from the first electrode in a longitudinal direction ona preset region of the insulating layer.